With the development of integrated circuit towards ultra-large scale integrated circuit, circuit density in the integrated circuit keeps increasing, the number of components included in the integrated circuit keeps increasing, and the size of the components decreases accordingly. With the decreasing of the size of metal-oxide-semiconductor (MOS) devices, channels of the MOS devices are shortened accordingly. Because the channel is shortened, the gradual channel approximation of the MOS devices is no longer valid, and varieties of adverse physical effects (especially the short-channel effect) become prominent. The device performance and reliability may degrade, limiting further reduction of the size of the devices.
To further reduce the size of the MOS devices, a multifaceted-gate field effect transistor (FET) structure has been developed to improve the control capability of the gate on the MOS device, and to suppress the short-channel effect. Among them, a FinFET is one of common multifaceted-gate field effect transistors.
The FinFET has a three-dimensional structure. The FinFET includes a substrate, one or more protruding fins formed on the substrate, and an insulating structure disposed between the adjacent fins. The FinFET also includes a gate crossing the one or more fins to cover the top and side surfaces of the fins. Because the three-dimensional FinFET is significantly different from the conventional planar transistor, improper operations in some processes may cause a great impact on the electrical properties of the formed device.
The threshold voltage of the transistor can be adjusted by implanting the doping ions into the channel region of the transistor. For the FinFET, the channel of the transistor is formed inside each fin. It is difficult to perform an ion implantation process onto the fin of the FinFET and to control concentration of doping ions in the fin, thus impacting the performance of the formed FinFET. The disclosed device structures and methods are directed to solve one or more problems set forth above and other problems.